Lithium batteries, such as lithium ion (Li-ion) batteries are attractive for stationary energy storage applications due to their fast response, high power capability, high efficiency, and long lifetime. The main components of a lithium ion battery are the electrodes (anode and cathode), electrolyte and a porous separator membrane. There are a wide variety of electrode materials, electrolytes and porous separator membrane materials available for use in rechargeable lithium batteries. Some lithium ion batteries use lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), or lithium iron phosphate (LFP or LiFePO4) as the cathode active material while the anodes may be made of carbon. Electrolytes can be organic or inorganic and facilitate the transfer of ions during the charge and discharge cycles. The separator can be a porous membrane that physically separates the anode from cathode and is ionically conductive (in electrolyte) and electronically insulating. The electrolyte is in close contact with the separator, and the separator pores should be fully wet by electrolyte for efficient movement of ions during charge and discharge cycles. The separator can be a microporous separator membrane made of a polyolefin. Polyolefins can be wet to a different degree by various organic and inorganic electrolytes. Charging capacity and battery performance are enhanced when the separator is quickly wet by an electrolyte.
Known separators may be microporous and made from polyolefins. Such polyolefin (PO) separators can provide excellent performance and safety in battery systems. Some polyolefin separators such as certain polypropylene (PP) separators are hydrophobic and may be less efficient at wetting or electrolyte filling in certain inorganic lithium ion battery systems. The proper wetting of a separator is necessary for the efficient movement of ions during cycling. Single layer non-woven separators have been utilized in certain inorganic battery systems but these non-wovens are typically too porous and may not adequately protect against shorts or dendrite growth.
Chemical treatments can alter the hydrophilicity of a polyolefin separator membrane, however, such treatments may not be permanent and/or unreactive in the electrolyte, as well as stable to any potential byproducts generated during repeated cycling of a rechargeable lithium ion battery. Hence, there is a need for improved separators that provide the high performance of a polyolefin membrane and the wettability of a nonwoven for at least certain battery chemistries or systems.